Genetics of reproductive performance across Porcine Reproductive and Respiratory Syndrome (PRRS) outbreak phases in purebred and crossbred sows

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BACKGROUND: Porcine Reproductive and Respiratory Syndrome (PRRS) is a major challenge for the worldwide pig industry. Therefore, genetic selection for enhanced disease resilience is a priority for pig breeding programs. The objectives of this study were to evaluate genetic variation in reproductive performance during a PRRS outbreak and to assess the impact of selecting for enhanced reproductive performance using data collected under non-challenged conditions on reproductive performance in a PRRS challenged environment. These objectives were addressed by identifying natural PRRS outbreak periods from longitudinal performance data and estimating genetic parameters for reproductive performance traits, before, during, and after a PRRS outbreak, using data collected from purebred and crossbred sows on multiplier farms. RESULTS: During PRRS outbreaks, the number of piglets born alive decreased, while the number of stillborn and mummified piglets increased for both purebred and crossbred sows. Additive genetic variance and heritability estimates for reproductive performance traits varied by phase. For most traits, additive genetic variance was highest during the outbreak. Estimates of genetic correlations between a given trait measured across phases ranged from 0.09 to 0.99, but were > 0.3 for most traits. In general, estimates of genetic correlations were greatest between a given trait before and after an outbreak. Results also indicated reranking of animals based on estimated breeding values across outbreak phases, with Spearman correlations below 0.50 for most traits and low proportion of top-ranking animals retained across phases. CONCLUSIONS: PRRS outbreak periods can be detected by evaluating phenotypic variation in reproductive performance from longitudinal data. Reproductive performance is heritable, whether evaluated before, during, or after a PRRS outbreak, but estimates varied by phase. Favorable moderate-to-high genetic correlations were estimated for reproductive performance traits measured before vs. during a PRRS outbreak, suggesting that selection for improved reproductive performance under non-challenged conditions is also expected to improve reproductive performance under PRRS challenge conditions. However, the estimates of genetic correlation for most of the reproductive traits indicated genotype-by-environment interactions between the PRRS-free and challenge conditions. Therefore, incorporating data collected under PRRS challenge will capture additional genetic variation in PRRS resilience and, ultimately, aid in selecting sows with increased PRRS resilience.

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